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Update device-pairing.md

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standards/application/device-pairing.md
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@ -37,7 +37,7 @@ and will share a Noise session within which they can securely exchange informati
The request is made by exposing a QR code that, by default, has to be scanned by device `A`.
If device `A` doesn't have a camera while device `B` does,
[it is possible](#Rationale) to execute a slightly different pairing (with same security guarantees),
[it is possible](#rationale) to execute a slightly different pairing (with same security guarantees),
where `A` is exposing a QR code instead.
This protocol is designed in order to achieve two main security objectives:
@ -82,19 +82,19 @@ d. -> sA, sAeB, sAsB {s}
- The content topic parameters `contentTopicParams = {application-name}, {application-version}, {shard-id}`.
- A (randomly generated) 16-bytes long `messageNametag`.
- A commitment `H(sB||r)` for its static key `sB` where `r` is a random fixed-lenght value.
- *** (Generate qr code?)***
2. The device `A`:
- *** (obtain qr code?)***
- scans the QR code;
- obtains `eB`, `contentTopicParams`, `messageNametag`, `Hash(sB||r)`;
- checks if `{application-name}` and `{application-version}` from `contentTopicParams` match the local application name and version: if not, aborts the pairing. Sets `contentTopic = /{application-name}/{application-version}/wakunoise/1/sessions_shard-{shard-id}/proto`;
- initializes the Noise handshake by passing `contentTopicParams`, `messageNametag` and `Hash(sB||r)` to the handshake prologue;
- executes the pre-handshake message, i.e. processes the key `eB`;
- executes the first handshake message over `contentTopic`, i.e.****
- processes and sends a Waku message containing an ephemeral key `eA`;***
- performs the pre-handshake process, i.e. processes the key `eB`;
- executes the first handshake message over `contentTopic`, i.e.
- processes and sends a [14/WAKU2-MESSAGE]() containing an ephemeral key `eA`;
- performs `DH(eA,eB)` (which computes a symmetric encryption key);
- attaches as payload to the handshake message the (encrypted) commitment `H(sA||s)` for `A`'s static key `sA`, where `s` is a random fixed-length value;
- attaches, as payload to the handshake message,
the (encrypted) commitment `H(sA||s)` for `A`'s static key `sA`, where `s` is a random fixed-length value;
- an 8-digits authorization code `authcode` obtained as `HKDF(h) mod 10^8` is displayed on the device, where `h` is the [handshake hash value](https://noiseprotocol.org/noise.html#overview-of-handshake-state-machine) obtained once the first handshake message is processed.
3. The device `B`:
@ -102,14 +102,14 @@ d. -> sA, sAeB, sAsB {s}
- sets `contentTopic = /{application-name}/{application-version}/wakunoise/1/sessions_shard-{shard-id}/proto`;
- listens to messages sent to `contentTopic` and locally filters only those with [Waku payload](./noise.md/#abnf) starting with `messageNametag`. If any, continues.
- initializes the Noise handshake by passing `contentTopicParams`, `messageNametag` and `Hash(sB||r)` to the handshake prologue;
- executes the pre-handshake message, i.e. processes its ephemeral key `eB`;****
- executes the first handshake message, i.e.*****
- performs the pre-handshake process, i.e. processes its ephemeral key `eB`;
- processes the received first handshake message, i.e.
- obtains from the received message a public key `eA`. If `eA` is not a valid public key, the protocol is aborted.
- performs `DH(eA,eB)` (which computes a symmetric encryption key);
- decrypts the commitment `H(sA||s)` for `A`'s static key `sA`.
- an 8 decimal digits authorization code `authcode` obtained as `HKDF(h) mod 10^8` is displayed on the device, where `h`is the [handshake hash value](https://noiseprotocol.org/noise.html#overview-of-handshake-state-machine) obtained once the first handshake message is processed.
4. Device `A` and `B` wait for the user to confirm with an interaction (button press)*******
4. Device `A` and `B` wait for user confirmations, through a user interface,
that the authorization code displayed on both devices are the same.
If not, the protocol is aborted.
@ -122,13 +122,13 @@ d. -> sA, sAeB, sAsB {s}
6. The device `A`:
- listens to messages sent to `contentTopic` and locally filters only those with [Waku](/)**** payload starting with `messageNametag`.
- listens to messages sent to `contentTopic` and locally filters only those with [26/WAKU2-PAYLOAD](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/application/26/payload.md) starting with `messageNametag`.
If any, continues.
- decrypts the received message and obtains the public key `sB`. If `sB` is not a valid public key, the protocol is aborted.
- performs `DH(eA,sB)` (which updates a symmetric encryption key);
- decrypts the payload to obtain the randomness `r`.
- computes `H(sB||r)` and checks if this value corresponds to the commitment obtained in step 2. If not, the protocol is aborted.
- executes the third handshake message, i.e.*****
- executes the third handshake message, i.e.
- processes and sends his (encrypted) device static key `sA` over `contentTopic`;
- performs `DH(sA,eB)` (which updates the symmetric encryption key);
- performs `DH(sA,sB)` (which updates the symmetric encryption key);
@ -137,12 +137,14 @@ d. -> sA, sAeB, sAsB {s}
7. The device `B`:
- listens to messages sent to `contentTopic` and locally filters only those with [**Waku](/) payload starting with `messageNametag`. If any, continues.
- obtains from decrypting the received message a public key `sA`. If `sA` is not a valid public key, the protocol is aborted.
- performs `DH(sA,eB)` (which updates a symmetric encryption key);
- performs `DH(sA,sB)` (which updates a symmetric encryption key);
- decrypts the payload to obtain the randomness `s`.
- Computes `H(sA||s)` and checks if this value corresponds to the commitment obtained in step 3. If not, the protocol is aborted.
- listens to messages sent to `contentTopic` and locally filters only those with [26/WAKU2-PAYLOAD](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/application/26/payload.md) starting with `messageNametag`. If any, continues.
- processess the third handshake message, i.e.
- obtains from decrypting the received message a public key `sA`. If `sA` is not a valid public key, the protocol is aborted.
- performs `DH(sA,eB)` (which updates a symmetric encryption key);
- performs `DH(sA,sB)` (which updates a symmetric encryption key);
- decrypts the payload to obtain the randomness `s`.
- Computes `H(sA||s)` and checks if this value corresponds to the commitment obtained in step 3.
If not, the protocol is aborted.
- Calls [Split()](http://www.noiseprotocol.org/noise.html#the-symmetricstate-object) and obtains two cipher states to encrypt inbound and outbound messages.
#### The `WakuPairing` for Devices without a Camera
@ -154,9 +156,9 @@ exchanging a single message (e.g., Noise sessions, cryptographic keys, signature
However, since the user(s) confirm(s) at the end of message `b.` that the authorization code is the same on both devices,
the role of the handhsake initiator and responder can be safely swapped in message `a.` and `b.`.
Indeed, if the pairing phase successfully completes on both devices,
the authentication code, the committed static keys and the Noise processing rules will ensure that no Man-in-the-Middle attack took place
and that messages can be securely exchanged bi-directionally in the transfer phase.
Indeed, if the pairing phase successfully completes on both devices, the authentication code,
the committed static keys and the Noise processing rules will ensure that no Man-in-the-Middle attack took place.
Messages can then be securely exchanged bi-directionally in the transfer phase.
This allows pairing in case device `A` does not have a camera to scan a QR (e.g. a desktop client) while device `B` has.
@ -259,7 +261,7 @@ in order to frequently and deterministically change the `messageNametag` of mess
ideally, at each message exchanged.
Given the proposed construction,
the `mntsInbound` and `mntsOutbound` secrets can be used to iteratively generate the `messageNametag` field of Waku payloads
the `mntsInbound` and `mntsOutbound` secrets can be used to iteratively generate the `messageNametag` field of [26/WAKU2-PAYLOAD](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/application/26/payload.md)s
for inbound and outbound messages, respectively.
The derivation of `messageNametag` should be deterministic only for communicating devices